Methods of producing para-xylene

ABSTRACT

The present disclosure provides methods to produce para-xylene, toluene, and other compounds from renewable sources (e.g., cellulose, hemicellulose, starch, sugar) and ethylene in the presence of a catalyst. For example, cellulose and/or hemicellulose may be converted into 2,5-dimethylfuran (DMF), which may be converted into para-xylene by cycloaddition of ethylene to DMF. Para-xylene can then be oxidized to form terephthalic acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application Ser. Nos. 61/611,114, filed Mar. 15, 2012, 61/651,594, filed May 25, 2012, and 61/701,276, filed Sep. 14, 2012, the disclosures of which are hereby incorporated by reference in their entireties.

FIELD

The present disclosure relates generally to the production of para-xylene and terephthalic acid, and more specifically to the production of para-xylene and terephthalic acid from renewable biomass resources (e.g., cellulose, hemicellulose, starch, sugar) and ethylene.

BACKGROUND

There exists a high demand to produce para-xylene and terephthalic acid from renewable biomass resources for use in the manufacture of clothing and plastics. Terephthalic acid is a precursor of polyethylene terephthalate (PET), which may be used to manufacture polyester fabrics. Terephthalic acid can be produced by oxidation of para-xylene.

Xylene is an aromatic hydrocarbon that occurs naturally in petroleum and coal tar. Commercial production of para-xylene is typically accomplished by catalyic reforming of petroleum derivatives. See e.g., U.S. Patent Application No. 2012/0029257. However, the use of petroleum-based feedstocks to commercially produce para-xylene (and hence terephthalic acid) generates greenhouse gas emissions and perpetuates reliance on petroleum resources.

Alternative methods to produce para-xylene from renewable biomass resources have been under investigation. Biomass containing cellulose and/or hemicellulose can be converted into DMF, and then DMF may be converted into para-xylene by Diels-Alder cycloaddition of ethylene. See e.g., U.S. Pat. No. 8,314,267; WO 2009/110402. The Diels-Alder conditions currently known in the art to produce para-xylene from cycloaddition of ethylene to DMF typically results in at least a portion of the DMF being converted into 2,5-hexanedione (HD), which generally polymerizes. Such a side reaction involving HD leads to a reduction of the selectivity to para-xylene. See e.g., Williams et al., ACS Catal. 2012, 2, 935-939; Do et al., ACS Catal. 2013, 3, 41-46.

Thus, what is needed in the art are alternative methods to produce para-xylene and terephthalic acid.

BRIEF SUMMARY

The present disclosure addresses this need by providing methods using particular catalysts, solvents, and reaction conditions to produce para-xylene from 2,5-dimethylfuran, 2,5-hexanedione, or a combination thereof. The para-xylene produced can then be oxidized to produce terephthalic acid.

In one aspect, provided is a method for producing para-xylene, by:

a) providing a starting material, wherein the starting material is 2,5-dimethylfuran (DMF), 2,5-hexanedione (HD), or a combination thereof;

b) providing ethylene;

c) providing a catalyst;

d) optionally providing a solvent;

e) combining the starting material with the ethylene, the catalyst, and optionally the solvent to form a reaction mixture; and

f) producing para-xylene from at least a portion of the DMF, HD, or a combination thereof in the reaction mixture.

In another aspect, provided is a method for producing para-xylene, by:

a) providing 2,5-dimethylfuran (DMF);

b) providing ethylene;

c) providing a catalyst;

d) providing a solvent;

e) combining the DMF with the ethylene, the catalyst, and the solvent to form a reaction mixture; and

f) producing para-xylene from at least a portion of the DMF in the reaction mixture.

In yet another aspect, provided is a method for producing para-xylene, by:

a) providing 2,5-hexanedione (HD);

b) providing ethylene;

c) providing a catalyst;

d) optionally providing a solvent;

e) combining the HD with the ethylene, the catalyst, and optionally the solvent to form a reaction mixture; and

f) producing para-xylene from at least a portion of the HD in the reaction mixture.

In some embodiments of any of the methods described above, the method further includes isolating para-xylene from the reaction mixture.

In some embodiments of any of the methods described above, the catalyst is a metal-containing catalyst. The catalyst may include a metal cation and counterion(s). The metal cation may be selected from, for example, Group 3, Group 9, Group 10, Group 11, or the lanthanide series. In certain embodiments, the catalyst includes a divalent metal cation or a trivalent metal cation. The divalent metal cation may be, for example, Cu²⁺, Co²⁺, Cr³⁺, Ni²⁺, Mg²⁺, or Zn²⁺. The trivalent metal cation may be, for example, Al³⁺, Bi³⁺, Fe³⁺, Gd³⁺, In³⁺, Nd³⁺, La³⁺, Sc³⁺, or Y³⁺. Suitable counterion(s) in the catalyst may include, for example, halides (e.g., chloride, bromide), triflates, and carboxylates (e.g. formate, acetate, acetylacetonate).

In some embodiments, the catalyst is selected from aluminum chloride, aluminum bromide, aluminum triflate, bismuth chloride, bismuth bromide, bismuth triflate, copper chloride, copper bromide, copper triflate, copper (II) bis(trifluoromethylsulfonyl)imide, cobalt chloride, cobalt bromide, cobalt triflate, chromium chloride, chromium bromide, chromium triflate, iron chloride, iron bromide, iron triflate, gadolinium chloride, gadolinium bromide, gadolinium triflate, indium chloride, indium bromide, indium triflate, nickel chloride, nickel bromide, nickel triflate, neodymium chloride, neodymium bromide, neodymium triflate, magnesium chloride, magnesium bromide, magnesium triflate, lanthanum chloride, lanthanum bromide, lanthanum triflate, scandium chloride, scandium bromide, scandium triflate, tin chloride, tin bromide, tin triflate, titanium chloride, titanium bromide, titanium triflate, vanadium chloride, vanadium bromide, vanadium triflate, yttrium chloride, yttrium bromide, yttrium triflate, zinc chloride, zinc bromide, zinc triflate, and any combinations thereof. In one embodiment, the catalyst is copper chloride, copper triflate, or yttrium triflate.

In other embodiments, the catalyst is a metal salt catalyst, including any such salts that may convert in situ into a species that is catalyst for the reactions described herein. For example, a metal salt catalyst may include a Group 11 metal with one or more counterion(s). The metal of the metal salt catalyst may be a copper cation. In one embodiment, the catalyst is copper acetate or copper acetylacetonate. As discussed above, any suitable counterions may be present in the metal salt catalyst.

In certain embodiments, the catalyst is unsupported. In other embodiments, the catalyst is solid supported. For example, one or more of the metal cations described above may be deposited on a solid support. Suitable supports include, for example, silica, alumina, mordenite, carbon (including, for example, activated carbon), and zeolites. In one embodiment, the catalyst may be copper (II) on mordenite, copper chloride on alumina, or copper chloride on HY zeolite. Such solid supported catalysts can more easily be recovered, recycled, and used in a continuous process.

In yet other embodiments, the catalyst may be an acid, including a Lewis acid or a weak acid. In yet other embodiments, the catalyst is a heteropolyacid. For example, in one embodiment, the catalyst is molybdosilicic acid or molybdophosphoric acid.

In some embodiments of any of the methods described above, the solvent system includes an aprotic solvent. The solvent may also be water-tolerant. The solvent may have one or more functional groups including, for example, ether, ester, ketone, alcohol, and halo.

In certain embodiments, the solvent system includes an ether, which may include cylic ethers, polyethers, glycol ethers, and other copolyethers. Suitable ether solvents may include dioxane, dioxin, glyme, diglyme, triglyme, tetrahydrofuran, and any combinations or mixtures thereof. In one embodiment, the solvent system includes 1,4-dioxane. In another embodiment, the solvent system includes triglyme.

In other embodiments, the solvent system includes dimethylacetamide, acetonitrile, sulfolane, dioxane, dioxane, dimethyl ether, diethyl ether, glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), tetrahydrofuran, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, triacetin, dibutylphthalate, butane, pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane, nonane, decane, undecane, dodecane, hexadecane, tetrachloride, chloroform, dichloromethane, nitromethane, toluene, anisole, nitrobenzene, bromobenzene, N-methylpyrrole, water, or any combinations or mixtures thereof. In one embodiment, the solvent system includes dioxane, dodecane, para-xylene, or any combinations or mixtures thereof.

In certain embodiments, the solvent system includes water, C6-C20 aliphatic solvents (which may be branched or linear), C6-C20 aromatic solvents, or alkyl benzene solvents. In one embodiment, the solvent system includes diphenyl ether or alkyldiphenyl ether.

In yet other embodiments, the solvent system includes an ionic liquid. Suitable ionic liquids may include, for example, 1-allyl-3-methylimidazolium bromide, 1-benzyl-3-methylimidazolium tetrafluoroborate, or any combination or mixture thereof.

It is understood that any description of catalyst for use in the methods described herein may be combined with any descriptions of the solvents the same as if each and every combination were individually listed.

For example, in some embodiments:

(i) the catalyst is a metal chloride, metal triflate, metal acetate or metal acetylacetonate; and

(ii) the solvent system includes an ether, a C₈₊ alkyl solvent (e.g., decane, dodecane), or para-xylene.

In some embodiments:

(i) the catalyst is a metal chloride, metal triflate, metal acetate or metal acetylacetonate; and

(ii) the solvent system includes an ether, a C₈₊ alkyl solvent (e.g., decane, dodecane), para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is a copper chloride, copper triflate, or yttrium triflate; and

(ii) the solvent system includes an ether, a C₈₊ alkyl solvent (e.g., decane, dodecane), para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is copper chloride, copper triflate, or yttrium triflate; and

(ii) the solvent system includes dioxane, dodecane, para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is a heteropolyacid; and

(ii) the solvent system includes an ether, a C₈₊ alkyl solvent (e.g., decane, dodecane), para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is a heteropolyacid; and

(ii) the solvent system includes dioxane, dodecane, para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is aluminum chloride; and

(ii) the solvent system includes an ether, a C₈₊ alkyl solvent (e.g., decane, dodecane), para-xylene, or any mixtures or combinations thereof.

In certain embodiments:

(i) the catalyst is aluminum chloride; and

(ii) the solvent system includes dioxane, dodecane, para-xylene, or any mixtures or combinations thereof.

In one embodiment:

(i) the catalyst is copper chloride, copper triflate, yttrium triflate, copper acetate or copper acetylacetonate; and

(ii) the solvent system includes dioxane, triglyme, or any mixtures or combinations thereof.

In one embodiment:

(i) the catalyst is copper triflate or yttrium triflate; and

(ii) the solvent system includes dioxane or triglyme.

In another embodiment:

(i) the catalyst is copper triflate or yttrium triflate; and

(ii) the solvent system includes a C₈₊ alkyl solvent (e.g., decane, dodecane).

In yet another embodiment:

(i) the catalyst is copper triflate or yttrium triflate; and

(ii) the solvent system includes para-xylene.

In yet another embodiment, the catalyst is copper triflate, and the solvent system includes an ether, such as dioxane or triglyme. In yet another embodiment, the catalyst is copper acetate or copper acetylacetonate, and the solvent system includes an ether, such as dioxane or triglyme.

It should further be understood that the catalyst/solvent combinations described above may be used for a reaction using HD as the starting material, DMF as the starting material, or both HD and DMF as the starting materials.

For example, in some embodiments, provided is a method for producing para-xylene, by:

a) providing a starting material, wherein the starting material is 2,5-dimethylfuran;

b) providing ethylene;

c) providing a catalyst, wherein the catalyst is a metal chloride, a metal triflate, a metal acetate, a metal acetylacetonate, or a heteropolyacid;

d) providing a solvent system, wherein the solvent system includes an ether, a C₈₊ alkyl solvent, an aromatic solvent, an ionic liquid, or any mixtures or combinations thereof;

e) combining the starting material, the ethylene, the solvent system and the catalyst to form a reaction mixture; and

f) producing para-xylene from at least a portion of the starting materials in the reaction mixture.

In certain embodiments to produce para-xylene from 2,5-dimethylfuran, the catalyst is copper chloride, copper triflate, yttrium triflate, copper acetate or copper acetylacetonate.

In certain embodiments to produce para-xylene from 2,5-dimethylfuran, the solvent system includes dioxane, dodecane, decane, para-xylene, diphenyl ether, alkyldiphenyl ether, or any mixtures or combinations thereof.

In other embodiments, provided is a method for producing para-xylene, by:

a) providing a starting material, wherein the starting material is 2,5-dimethylfuran, 2,5-hexanedione, or a combination thereof;

b) providing ethylene;

c) providing a catalyst, wherein the catalyst is a heteropolyacid;

d) providing a solvent system;

e) combining the starting material, the ethylene, the solvent system and the catalyst to form a reaction mixture; and

f) producing para-xylene from at least a portion of the starting materials in the reaction mixture.

In certain embodiments to produce para-xylene from 2,5-dimethylfuran, 2,5-hexanedione, or a combination thereof, the solvent system includes dioxane, dodecane, decane, para-xylene, diphenyl ether, alkyldiphenyl ether, or any mixtures or combinations thereof.

In yet other embodiments, at least a portion of the DMF (if present), HD (if present), or a combination thereof is converted to para-xylene at a temperature of at least 150° C., or between 150° C. and 300° C.

The para-xylene produced by any of the methods described above may be used for the manufacture of a plastic or a fuel.

Provided is also a method for producing terephthalic acid, by:

a) producing para-xylene according to any of the methods described herein; and

b) oxidizing the para-xylene to produce terephthalic acid.

DETAILED DESCRIPTION

The following description sets forth numerous exemplary configurations, methods, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure, but is instead provided as a description of exemplary embodiments.

The following description relates to methods of producing para-xylene (PX) from 2,5-dimethylfuran (DMF), 2,5-hexanedione (HD), or a combination thereof. Provided is a method for producing para-xylene, by: a) providing DMF, HD, or a combination thereof; b) providing ethylene; c) providing a catalyst; d) optionally providing a solvent; e) combining the DMF, HD, or a combination with the ethylene, the catalyst, and optionally the solvent to form a reaction mixture; and f) producing para-xylene from at least a portion of the DMF, HD, or a combination thereof in the reaction mixture.

The use of the particular catalysts, solvents, and reaction conditions provided herein allow for either DMF or HD, or a combination thereof, to serve as a starting material for production of para-xylene.

Starting Materials

2,5-Dimethylfuran (DMF) and 2,5-hexanedione (HD) may both, either alone or in combination, be used as starting materials for the production of para-xylene according to the methods described herein. The DMF and HD provided for the methods described herein can be obtained from any source (including any commercially available sources), or be produced by any methods known in the art. Similarly, ethylene is also a starting material for this reaction. The ethylene provided for the methods described herein may be obtained from any source (including any commercially available sources). For example, ethylene can be obtained from fossil fuel sources or renewable sources, such as by dehydration of ethanol (e.g., fermentation-based ethanol).

a) DMF

DMF used in the methods described herein may be commercially available, or be derived from carbonaceous materials. Examples of suitable carbonaceous materials from which DMF can be derived include agricultural materials (e.g., corn stover, rice hulls, peanut hulls, spent grains, pine chips), processing waste (e.g., paper sludge), recycled cellulosic materials (e.g., cardboard, old corrugated containers (OCC), mixed paper, old newspaper (ONP)), as well as fructose (e.g., high fructose corn syrup), sucrose, glucose, or starch.

Various methods are known in the art to obtain DMF from biomass. For example, cellulose and hemicellulose (if present) or other six-carbon sugars (e.g., glucose, fructose) may be converted into 5-chloromethylfurfural, which may be converted into DMF either directly or via 5-hydroxymethylfurfural. See e.g., Chidambaram & Bell, Green Chem., 2010, 12, 1253-1262.

b) HD

HD (also known as acetonyl acetone) used in the methods described herein may be commercially available, or be prepared according to methods known in the art. For example, it is known that HD can be prepared by oxidization of allylacetone. See U.S. Pat. No. 3,947,521. HD can also be prepared by hydrolysis of the lactone of alpha-acetyl-gamma-cyano-gamma-hydroxyvaleric acid. See U.S. Pat. No. 3,819,714.

Catalysts

Various catalysts may be used in the method to convert DMF and/or HD into para-xylene. For example, the catalysts may be selected from one or more classes of catalysts, including (i) metal-containing catalysts, including metal-containing salts that are catalytic or may convert in situ into a catalytic species, and (ii) acids (e.g., Lewis acids, weak acids, heteropolyacids). It should be understood, however, that the catalyst may fall into one or more classes listed herein. For example, the catalyst may be copper triflate, which is a metal-containing catalyst and also a Lewis acid. The catalyst may also be supported or unsupported. The catalyst may also be homogeneous or heterogeneous based on the solvent system used in the reaction. The catalysts may also be in the form of a solvate, including, for example, a hydrate.

The catalysts provided for the methods described herein to produce para-xylene may be obtained from any sources (including any commercially available sources), or may be prepared by any methods or techniques known in the art. It should also be understood that providing a catalyst includes providing the catalyst itself, or a precursor that forms the catalytic species (e.g., in situ).

Metal Catalysts

In some embodiments, the catalyst is a metal catalyst. A metal catalyst can be any catalyst that is a metal or contains a metal ligand. The metals may include a transition metal or a lanthanide. In certain embodiments, the metal is selected from Group 3, Group 9, Group 10, Group 11, or the lanthanide series. In certain embodiments, the metal is selected from Group 3, Group 9, Group 11, or the lanthanide series.

The catalytic species used in the reactions described herein may also be formed in situ by providing the suitable precursors. For example, copper metal and chlorine gas may be provided to the reaction to produce copper chloride in situ. It should also be understood that the catalytic species may be formed in situ by reaction between the metal precursor and the ethylene provided in the reaction. For example, a copper triflate may be provided to the reaction, and may form a catalytic species with ethylene.

In one embodiment, the metal catalyst is a metal-containing catalyst. Metal-containing catalysts have one or more metal cations and one or more counterions or ligands. For example, the catalyst may be a metal-centered catalyst. The metal cation may be a transition metal cation or a lanthanide cation. In certain embodiments, the metal cation is selected from Group 3, Group 9, Group 10, Group 11, or the lanthanide series. In certain embodiments, the metal cation is selected from Group 3, Group 9, Group 11, or the lanthanide series. In one embodiment, the metal cation is a Group 11 cation. It should be understood that the group number used for the metals follow the IUPAC or long-form nomenclature, which is well-known in the art.

The catalyst may have a divalent metal cation or a trivalent metal cation. For example, in some embodiments, the divalent metal cation is Cu²⁺, Co²⁺, Cr³⁺, Ni²⁺, Mg²⁺, or Zn²⁺. In certain embodiments, the divalent metal cation is Cu²⁺, Co²⁺, Ni²⁺, or Zn²⁺. In one embodiment, the divalent metal cation is Cu²⁺, Co²⁺, or Zn²⁺. In one embodiment, the divalent metal cation is Cu²⁺. In some embodiments, the trivalent metal cation is Al³⁺, Bi³⁺, Fe³⁺, Gd³⁺, In³⁺, Nd³⁺, La³⁺, Sc³⁺, or Y³⁺. In certain embodiments, the trivalent metal cation is Al³⁺, Fe³⁺, Gd³⁺, In³⁺, La³⁺, or Y³⁺. In one embodiment, the trivalent metal cation is Al³⁺, Gd³⁺, In³⁺, La³⁺, or Y³⁺. In another embodiment, the trivalent metal cation is Gd³⁺, In³⁺, La³⁺, or Y³⁺.

The divalent or trivalent metal cation of the catalyst may coordinate with two or three counterions, respectively. Each counterion may independently be selected from, for example, halides (e.g., chloride, bromide), triflates (—OTf), and carboxylates (e.g. formate, acetate, acetylacetonate). It should be understood, however, that any suitable counterion may be used. In one embodiment, the counterions may be chloride or triflate. It should be understood that the counterions may all be the same, the counterions may all be different, or two counterions may be the same and the third counterion may be different.

In some embodiments, the counterions may be ligands that coordinate with the metal. Ligands may be, cationic, anionic or neutral. For example, the catalyst may be η²-ethylene-copper(II)triflate.

In some embodiments, the catalyst is aluminum chloride, aluminum bromide, aluminum triflate, bismuth chloride, bismuth bromide, bismuth triflate, copper chloride, copper bromide, copper triflate, cobalt chloride, cobalt bromide, cobalt triflate, chromium chloride, chromium bromide, chromium triflate, iron chloride, iron bromide, iron triflate, gadolinium chloride, gadolinium bromide, gadolinium triflate, indium chloride, indium bromide, indium triflate, nickel chloride, nickel bromide, nickel triflate, neodymium chloride, neodymium bromide, neodymium triflate, magnesium chloride, magnesium bromide, magnesium triflate, lanthanum chloride, lanthanum bromide, lanthanum triflate, scandium chloride, scandium bromide, scandium triflate, tin chloride, tin bromide, tin triflate, titanium chloride, titanium bromide, titanium triflate, vanadium chloride, vanadium bromide, vanadium triflate, yttrium chloride, yttrium bromide, yttrium triflate, zinc chloride, zinc bromide, zinc triflate, or any combinations thereof.

In certain embodiments, the catalyst is copper chloride, copper triflate, yttrium triflate, scandium triflate, lanthanum triflate, neodymium triflate, copper triflimide, or any combinations thereof. In other embodiments, the catalyst is aluminum chloride, copper chloride, copper triflate, yttrium triflate, or any combination thereof. In one embodiment, the catalyst is copper chloride or copper triflate, or a combination thereof. In another embodiment, the catalyst is copper (II) bis(trifluoromethylsulfonyl)imide (i.e., copper triflimide).

In other embodiments, the catalyst is a metal-containing salt catalyst, including any such salts that may convert in situ into a species that is catalyst for the reactions described herein. For example, a metal salt catalyst may include a Group 11 metal with one or more counterion(s). The metal of the metal salt catalyst may be a copper cation. In one embodiment, the catalyst is copper acetate or copper acetylacetonate. As discussed above, any suitable counterions may be present in the metal-containing salt catalyst.

Lewis Acids

In some embodiments, the catalyst is a Lewis acid. As used herein, a “Lewis acid” refers to an acid substance that can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms.

It should be understood that one or more of the metal-containing catalysts described above may be Lewis acids. For example, the catalyst may be a Lewis acid, such as aluminum chloride, zinc chloride, indium chloride, divalent transition metal ions of copper, nickel or cobalt or mixtures thereof such as CuCl₂ or CoCl₂, triflates such as the triflate of indium, copper, gadolinium or yttrium, trivalent metal ions from the lanthanide series of elements or mixtures thereof.

In other embodiments, the catalysts may also include acetic acid, haloacetic acid (e.g., chloroacetic acid, dichloroacetic acid, trichloroacetic acid, fluoroacetic acid, and difluoroacetic acid, trifluoroacetic acid). These acids may be Lewis acids in the reaction. The acids may also be obtained from an anhydride that hydrolyzes into its corresponding acid form in the presence of water. For example, acetic anhydride may contain a small percentage of acetic acid, which acts as a catalyst for the reaction. Additionally, the acetic anhydride in the reaction mixture may further convert into acetic acid in the reaction.

Heteropolyacids

In other embodiments, the Lewis acid is a heteropolyacid. Heteropolyacids is a class of acids that includes a combination of hydrogen and oxygen atoms with certain metals and/or non-metals. The heteropolyacid typically includes at least one addenda atom, oxygen, a hetero atom, and acidic hydrogen atoms. In certain embodiments, the addenda atoms may be selected from one or more metals, including for example, tungsten, molybdenum, or vanadium. In certain embodiments, the hetero atom may be selected from p-block elements, such as silicon or phosphorous. It is understood that any description of the addenda atoms for the heteropolyacids for use in the methods described herein may be combined with any descriptions of the hetero atoms the same as if each and every combination were specifically and individually listed. Suitable heteropolyacids may include, for example, tungstosilicic acid, tungostophosphoric acid, molybdosilicic acid, molybdophosphoric acid. A mixture of heteropolyacids may also be used.

The heteropolyacids may have certain structures that are known in the art. In one embodiment, the heteropolyacid is a Keggin structure, having the formula H_(n)XM₁₂O₄₀, where X is the hetero atom, M is the addenda atom, and n is an integer greater than 0. In another embodiment, the heteropolyacid is a Dawson structure having the formula H_(n)X₂M₁₈O₆₂, where X is the hetero atom, M is the addenda atom, and n in an integer greater than 0.

In one embodiment, the catalyst is a heteropolyacid selected from 12-tungstophosphoric acid, 12-molybdophosphoric acid, 12-tungstosilicic acid, 12-molybdosilicic acid, and any combinations thereof.

In certain embodiments, the catalyst may be a solvate of a heteropolyacid. Suitable solvates may include hydrates or alcohol solvates.

In other embodiments that may be combined with any of the foregoing embodiments, the catalyst that is a heteropolyacid may be unsupported or supported. In one embodiment, the catalyst is a supported heteropolyacid. Suitable solid supports for the heteropolyacids may include, for example, carbon, alumina, silica, ceria, titania, zirconia, niobia, zeolite, magnesia, clays, iron oxide, silicon carbide, aluminosilicates, and any modifications, mixtures or combinations thereof.

Water-Tolerant Catalysts

In some embodiments, the catalysts may also be water-tolerant catalysts. As used herein, “a water-tolerant catalyst” refers to a catalyst that is not deactivated by the presence of water in a given reaction. One of skill in the art would recognize that a given catalyst may show water stability for the purposes of one reaction, but not toward another. Water-tolerant catalyst can improve recyclability of the catalyst used in the reaction on industrial scale, since water can often be produced as a by-product in the reaction. In some embodiments, the water-tolerant catalyst may have a pK_(h) between 4.3 and 10.08. K_(b) is the hydrolysis constant. pK_(h) is defined as follows:

pK_(h) = −log  K_(xy), where ${{Kxy} = {\frac{{\left\lbrack {M_{x}({OH})}_{y}^{{({{xz} - y})} +} \right\rbrack\left\lbrack H^{+} \right\rbrack}^{y}}{\left\lbrack M^{z +} \right\rbrack^{x}}*\frac{g_{xy}g_{H^{+}}^{y}}{g_{M^{z +}}^{x}a_{H_{2}O}^{y}}}},$ based on the following reaction: xM²⁺+yH₂O⇄M_(x)(OH)_(y) ^((xz-y)+)+yH⁺, where M is the metal cation. In other embodiments, the water-tolerant catalyst may have a water exchange rate constant of at least 3.2×10⁶ M⁻¹s⁻¹. See generally Kobayashi et al., J. Am. Chem. Soc. 1998, 120, 8287-8288.

Examples of water-tolerant catalysts may include those with a metal cation selected from Sc(III), Y(III), Ln(III), Fe(II), Cu(II), Zn(II), Cd(II), Pb(II), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III). In certain embodiments, the catalyst may include Fe(II), Cu(II), Zn(II), Cd(II), Pb(II), Sc(III), Y(III), Ln(III), Mn(II), or Ag(I). Water-tolerant catalysts may include, for example, ScCl₃, Sc(ClO₄)₃, Mn(ClO₄)₂, FeCl₂, Fe(ClO₄)₂, FeCl₃, Fe(ClO₄)₃, Co(ClO₄)₂, Ni(ClO₄)₂, CuCl₂, Cu(ClO₄)₂, ZnCl₂, Zn(ClO₄)₂, YCl₃, Y(ClO₄)₃, AgClO₄, CdCl₂, Cd(ClO₄)₂, InCl₃, In(ClO₄)₃, SnCl₂, La(OTf)₃, Ce(OTf)₃, Pr(OTf)₃, Nd(OTf)₃, Sm(OTf)₃, Eu(OTf)₃, Gd(OTf)₃, Tb(OTf)₃, Dy(OTf)₃, Ho(OTf)₃, Er(OTf)₃, Tm(OTf)₃, YbCl₃, Yb(ClO₄)₃, Yb(OTf)₃, Lu(OTf)₃, PbCl₂, and Pb(ClO₄)₂.

Supported or Unsupported Catalysts

Any of the catalysts described above may be unsupported or supported. In one embodiment, the catalyst is unsupported. In another embodiment, the catalyst is supported by a solid support. Suitable supports may include, for example, carbon, alumina, silica, ceria, titania, zirconia, niobia, zeolite, magnesia, clays, iron oxide, silicon carbide, aluminosilicates, and any modifications, mixtures or combinations thereof. In certain embodiments, the support is silica, alumina, mordenite, carbon (including, for example, activated carbon), or zeolites (e.g., HY zeolite). Examples of supported catalyst may include copper on mordenite, alumina or zeolite. In one embodiment, the catalyst is copper (II) on mordenite, copper chloride on silica, copper chloride on alumina, or copper chloride on HY zeolite. In another embodiment, the support is activated carbon. The activated carbon may also be further treated, for example, acid treated (e.g., H₃PO₄ treated).

Solid supported catalysts can more easily be recovered, recycled, and used in a continuous process. When a catalyst support is used, the metals may be deposited using any procedures known in the art. See e.g., Schwarz et al., Chem. Rev. 95, 477-510, (1995).

Homogeneous or Heterogeneous Catalysts

In some embodiments, the catalyst is homogeneous in the reaction mixture. As used herein, a “homogeneous catalyst” refers to a catalyst that substantially dissolves in the reaction mixture under the reaction conditions. For example, acetic acid as the catalyst substantially dissolves in dioxane. In another example, copper triflate substantially dissolves in dodecane under the reaction conditions, but not at all conditions (e.g., at standard, temperature and pressure). A catalyst is “substantially dissolved” when the amount of dissolved catalyst exceeds the quantity of undissolved catalyst at the reaction conditions. In some embodiments, the catalyst is substantially dissolved when the ratio of amount of undissolved catalyst to the amount of dissolved catalyst is between 0:1 and 1:1 at the reaction conditions. In one embodiment, the ratio of amount of undissolved catalyst to the amount of dissolved catalyst is about 0 at the reaction conditions. Any suitable methods may be used to determine or quantify the solubility of catalyst.

In other embodiments, the catalyst is heterogeneous in the reaction. As used herein, a “heterogeneous catalyst” refers to any catalyst that is not a heterogeneous catalyst as described above.

It should be understood that the homogeneity or heterogeneity of a catalyst may depend on the solvent or solvent mixtures used, as well as the reaction conditions.

Solvent Systems

A solvent, or a combination or mixture of solvents, may also be optionally added to the reaction mixture. The solvents used in the methods described herein may be obtained from any source, including any commercially available sources. In some embodiments, the methods described herein use certain solvents to convert DMF, HD, or a combination thereof, into para-xylene with yields of at least 50%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% on a molar basis.

The particular solvents used in the methods described herein typically can solubilize, or at least partially solubilize, the starting materials (e.g., DMF, HD or a combination thereof, ethylene) and/or catalysts, which can help to enhance the solvation effect and improve the reaction rate. For example, in some embodiments, the solvent have an ethylene solubility between about 0 mol/L and about 0.82 mol/L, between about 0.82 mol/L and about 1.2 mol/L, or between about 1.2 mol/L and about 4.0 mol/L, when ethylene solubility is measured a temperature of 23° C.

The solvents used may also be selected based on their boiling points. The solvents may be selected based on their boiling points at standard pressure or operating pressure. In some embodiments, the solvent may have a boiling point of between 80° C. and 400° C., or between 150° C. and 350° C. Further, the solvent selected may have a boiling point higher than para-xylene. This would allow para-xylene to be distilled from the reaction mixture, leaving the catalyst and solvent behind to be recycled and/or recovered.

Additionally, the solvents are typically stable to the process conditions, and preferably can be recycled for use again in the reaction. The recyclability of the solvent is particularly useful for performing the methods described herein on a commercial scale.

The solvents used herein may be aliphatic or aromatic. The solvents may also have one or more functional groups such as halo, ester, ether, ketone, and alcohol, or any combinations or mixtures thereof. The solvent may also be non-cyclic (including linear or branched) or cyclic. While the different classes of solvents are described below (e.g., aprotic solvents, aliphatic solvents, aromatic solvents, alkyl phenyl solvents, ether solvents, alcohol solvents, ketone solvents, haloginated solvents, or ionic liquids), it should be understood that the solvent may fall within one or more classes described. For example, dioxane is an ether that is aprotic.

In one embodiment, the solvent system includes dimethylacetamide, acetonitrile, sulfolane, dioxane, dioxane, dimethyl ether, diethyl ether, glycol dimethyl ether (monoglyme), ethylene glycol diethyl ether (ethyl glyme), diethylene glycol dimethyl ether (diglyme), diethylene glycol diethyl ether (ethyl digylme), triethylene glycol dimethyl ether (triglyme), diethylene glycol dibutyl ether (butyl diglyme), tetraethylene glycol dimethyl ether (tetraglyme), polyglyme, proglyme, highlyme, tetrahydrofuran, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, triacetin, dibutylphthalate, butane, pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane, nonane, decane, undecane, dodecane, hexadecane, tetrachloride, chloroform, dichloromethane, nitromethane, toluene, anisole, nitrobenzene, bromobenzene, N-methylpyrrole, para-xylene, mesitylene, dodecylbenzene, pentylbenzene, hexylbenzene, Wibaryl® A, Wibaryl® B, Wibaryl® AB, Wibaryl® F, Wibaryl® R, Cepsa Petrepar®550-Q, diphenyl ether, methyldiphenyl ether, ethyldiphenyl ether, water, or any combinations or mixtures thereof.

In certain embodiments, the solvent system includes dioxane, tetrahydrofuran, sulfolane, triglyme, or any combinations or mixtures thereof. In one preferred embodiment, the solvent system includes 1,4-dioxane. In other embodiments, the solvent system includes a glyme. For example, in one embodiment, the solvent system includes triglyme. Any of the above indicated solvents which have these same properties as dioxane or triglyme may be used as a solvent in the methods described herein.

Aprotic Solvents

In some embodiments, the solvent system includes an aprotic solvent. For example, the aprotic solvent may have a dipole moment above 0.1. One of skill in the art would understand that the dipole moment is a measure of polarity of a solvent. The dipole moment of a liquid can be measured with a dipole meter. Suitable aprotic solvents may include, for example, dimethylacetamide, dioxane, polyethers (including, for example, glyme, diglyme, triglyme, tetraglyme), acetonitrile, sulfolane, ethers (including, for example, tetrahydrofuran, dialkylether (e.g., dimethylether, diethylether), nitromethane, anisole, nitrobenzene, bromobenzene, or any combinations or mixtures thereof.

Aliphatic Solvents

In one embodiment, the solvent system includes an aliphatic solvent. The aliphatic solvent may be linear, branched, or cyclic. The aliphatic solvent may also be saturated (e.g., alkane) or unsaturated (e.g., alkene or alkyne). In some embodiments, the solvent system includes a C1-C20 aliphatic solvent, a C1-C10, aliphatic solvent, or a C1-C6 aliphatic solvent. In certain embodiments, the solvent system includes a C8+ alkyl solvent, or a C8-C50 alkyl solvent, a C8-C40 alkyl solvent, a C8-C30 alkyl solvent, a C8-C20 alkyl solvent, or a C8-C16 alkyl solvent. Suitable aliphatic solvents may include, for example, butane, pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane, nonane, decane, undecane, dodecane, hexadecane, or any combinations or mixtures thereof.

Aromatic Solvents

In another embodiment, the solvent system includes an aromatic solvent. In some embodiments, the solvent system includes a C6-C20 aromatic solvent, a C6-C12 aromatic solvent, or a C13-C20 aromatic solvent. The aromatic solvent may be optionally substituted. Suitable aromatic solvents may include, for example, toluene, anisole, nitrobenzene, bromobenzene, and N-methylpyrrole. In one embodiment, the solvent system includes para-xylene (which may be produced in the reaction or provided to the reaction system).

Alkyl Phenyl Solvents

As used herein, “an alkyl phenyl solvent” refers to a class of solvents that may have one or more alkyl chains and one or more phenyl or phenyl-containing ring systems. The alkyl phenyl solvent may be referred to as an alkylbenzene or a phenylalkane. One skilled in the art would recognize that certain phenylalkanes may also be interchangeably referred to as an alkylbenzene. For example, (1-phenyl)pentane and pentylbenzene refer to the same solvent.

In some embodiments, the solvent system includes an alkylbenzene. Examples may include (monoalkyl)benzenes, (dialkyl)benzenes, and (polyalkyl)benzenes. In certain embodiments, the alkylbenzene has one alkyl chain attached to one benzene ring. The alkyl chain may have one or two points of attachment to the benzene ring. Examples of alkylbenzenes with one alkyl chain having one point of attachment to the benzene ring include pentylbenzene, hexylbenzene and dodecylbenzene. In embodiments where the alkyl chain has two points of attachment to the benzene ring, the alkyl chain may form a fused cycloalkyl ring to the benzene. Examples of alkylbenzenes with one alkyl having two points of attachment to the benzene ring include tetralin. It should be understood that the fused cycloalkyl ring may be further substituted with one or more alkyl rings.

In other embodiments, the alkylbenzene has two or more alkyl chains (e.g., 2, 3, 4, 5, or 6 alkyl chains) attached to one benzene ring.

In yet other embodiments, the alkylbenzene is an alkyl-substituted fused benzene ring system. The fused benzene ring system may include benzene fused with one or more heterocyclic rings. In one embodiment, the fused benzene ring system may be two or more fused benzene rings, such as naphthalene. The fused benzene ring system may be optionally substituted by one or more alkyl chains.

In some embodiments, the solvent system includes phenylalkane. Examples may include (monophenyl)alkanes, (diphenyl)alkanes, and (polyphenyl)alkanes. In certain embodiments, the phenylalkane has one phenyl ring attached to one alkyl chain. The phenyl ring may be attached to any carbon along the alkyl chain. For example, the phenyl alkyl having one alkyl chain may be (1-phenyl)pentane, (2-phenyl)pentane, (1-phenyl)hexane, (2-phenyl)hexane, (3-phenyl)hexane, (1-phenyl)dodecane, and (2-phenyl)dodecane.

In other embodiments, the phenylalkane has two or more phenyl rings attached to one alkyl chain.

In one embodiment, the solvent system includes Wibaryl® A, Wibaryl® B, Wibaryl® AB, Wibaryl® F, Wibaryl® R, Cepsa Petrepar® 550-Q, or any combinations or mixtures thereof.

“Alkyl” refers to a monoradical saturated hydrocarbon chain. The length of the alkyl chain may vary. In certain embodiments, the alkyl chain may be 1 to 20 carbon atoms (e.g., C₁₋₂₀ alkyl). In one embodiment, the alkyl chain may be 4 to 15 carbons (e.g., C₄₋₁₅ alkyl), or 10 to 13 carbons (e.g., C₁₀₋₁₃ alkyl).

The alkyl chain may be linear or branched. Linear alkyl chains may include, for example, n-propyl, n-butyl, n-hexyl, n-heptyl, n-octyl, n-nonanyl, n-decyl, n-undecyl, and n-dodecyl. Branched alkyl chains may include, for example, isopropyl, sec-butyl, isobutyl, tert-butyl, and neopentyl. In some embodiments where the solvent includes two or more alkyl chains, certain alkyl chains may be linear, whereas other alkyl chains may be branched. In other embodiments where the solvent includes two or more alkyl chains, all the alkyl chains may be linear or all the alkyl chains may be branched.

For example, the solvent system includes a linear alkylbenzene (“LAB”). Linear alkylbenzenes are a class of solvents having the formula C₆H₅C_(n)H_(2n+1). For example, in one embodiment, the linear alkylbenzene is dodecylbenzene. Dodecylbenzene is commercially available, and may be “hard type” or “soft type”. Hard type dodecylbenzene is a mixture of branched chain isomers. Soft type dodecylbenzene is a mixture of linear chain isomers. In one embodiment, the solvent system includes a hard type dodecylbenzene.

In some embodiments, the solvent system includes any of the alkyl phenyl solvents described above, in which the phenyl ring is substituted with one or more halogen atoms. In certain embodiments, the solvent system includes an alkyl(halobenzene). For example, the alkyl(halobenzene) may include alkyl(chlorobenzene). In one embodiment, the halo substituent for the phenyl ring may be, for example, chloro, bromo, or any combination thereof.

In other embodiments, the solvent system includes naphthalene, naphthenic oil, alkylated naphthalene, diphenyl, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, or haloginated hydrocarbons.

Ether Solvents

In other embodiments, the solvent system includes an ether solvent, which refers to a solvent having at least one ether group. For example, the solvent system includes a C2-C20 ether, or a C2-C10 ether. The ether solvent can be non-cyclic or cyclic. For example, the ether solvent may be alkyl ether (e.g., diethyl ether, glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), or triethylene glycol dimethyl ether (triglyme)). In another example, the ether solvent may be cyclic, such as dioxane (e.g., 1,4-dioxane), dioxin, tetrahydrofuran, or a cycloalkyl alkyl ether (e.g., cyclopentyl methyl ether).

The solvent system may include an acetal such as dioxolane (e.g., 1,3-dioxolane).

The solvent system may also include a polyether with two or more oxygen atoms. In some embodiments, the ether solvent has a formula as follows:

where each R_(a) and R_(b) are independently aliphatic moieties, and n and m are integers equal to or greater than 1. In some embodiments, each R_(a) and R_(b) are independently alkyl. In certain embodiments, each R_(a) and R_(b) are independently C1-C10 alkyl, or C1-C6 alkyl. R_(a) and R_(b) may be the same or different. In other embodiments, each n and m are independently 1 to 10, or 1 to 6, where n and m may be the same or different.

The formula above includes proglymes (such as dipropylene glycol dimethylether), or glymes (such as glycol diethers based on ethylene oxide). In one embodiment, the solvent system includes glyme, diglyme, triglyme, or tetraglyme.

It should also be understood that a solvent having an ether group may also have one or more other functional groups. It should be understood, however, that the solvent may have an ether functional group in combination with one or more additional functional groups, such as alcohols. For example, the solvent system includes alkylene glycols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol), phenyl ethers (e.g., diphenyl ether), or alkylphenylethers (e.g., alkyldiphenyl ether).

Ester Solvents

In yet other embodiments, the solvent system includes an ester solvent, which refers to a solvent having at least one ester group. For example, the solvent system includes a C2-C20 ester, or a C2-C10 ester. The ester solvent can be non-cyclic (linear or branched) or cyclic. For example, non-cyclic ester solvents may include alkyl acetate (e.g., methyl acetate, ethyl acetate, propyl acetate, butyl acetate), triacetin, and dibutylphthalate. An example of cyclic ester is, for example, propylene carbonate. It should be understood, however, that a solvent having an ester group may also have one or more other functional groups. The ester solvent may also include alkyl lactate (e.g., methyl lactate, ethyl lactate, propyl lactate, butyl lactate), which has both an ester group as well as a hydroxyl group.

Alcohol Solvents

In yet other embodiments, the solvent system includes an alcohol, which refers to a solvent having at least hydroxyl group. For example, the solvent can be a C1-C20 alcohol, a C1-C10 alcohol, or a C1-C6 alcohol. Alcohol solvents may include, for example, methanol, ethanol and propanol. The solvent may also be an alkanediol, such as 1,3-propanediol or propylene glycol.

Ketone Solvents

It yet other embodiments, the solvent system includes a ketone. For example, the solvent can be a C2-C20 ketone, a C2-C10 ketone, or a C2-C6 ketone. The ketone solvent can be non-cyclic (linear or branched) or cyclic. For example, the solvent system includes cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, or cyclooctanone.

Halogenated Solvents

In yet other embodiments, the solvent system includes haloginated solvents. For example, the solvent can be a chlorinated solvent. Suitable chlorinated solvents may include, for example, carbon tetrachloride, chloroform and methylene chloride.

Ionic Liquids

The solvent may also be an ionic liquid. Suitable ionic liquids may include, for example, 1-allyl-3-methylimidazolium bromide and 1-benzyl-3-methylimidazolium tetrafluoroborate.

Solvent Combinations or Mixtures

A combination or mixture of solvents may also used in the methods described herein. In some embodiments, an ether solvent may be combined with one or more other types of solvents listed above, including for example an aliphatic solvent. In one embodiment, the solvent combination or mixture is dioxane and an aliphatic solvent. For example, the solvent combination is dioxane and dodecane.

Amount of Solvent

The amount of solvent used may vary depending on the starting materials, catalyst used, and reaction conditions. For example, in some embodiments, the concentration of the DMF and/or HD in the reaction mixture is from about 1 to about 75% by weight in the solvent, or from about 3 to about 50% by weight in the solvent.

Reaction Conditions

In some embodiments, the reaction temperature may be at least 150° C., or at least 200° C. In other embodiments, the reaction temperature may be between 100° C. and 300° C., between 150° C. and 400° C., between 150° C. and 300° C., between 125° C. and 175° C., between 200° C. to 350° C., between 200° C. to 250° C., between 200° C. and 400° C., between 220° C. to 230° C., between 250° C. to 300° C., or between 150° C. and 220° C. In one embodiment, the reaction temperature is between room temperature (e.g., 18° C.-22° C.) and 300° C. Higher temperatures can be used provided that the solvent selected is stable.

In some embodiments, the reaction may proceed at a pressure between 1 bar and 1000 bar, between 10 bar to 1000 bar, between 20 bar to 1000 bar, between 50 bar to 1000 bar, between 100 bar to 1000 bar, between 150 bar to 500 bar, between 35 and 38 bar, between 1 bar and 50 bar, between 1 bar and 40 bar, between 1 bar and 30 bar, between 1 bar and 20 bar, between 1 bar and 10 bar, between 1 bar and 5 bar, between 5 bar and 30 bar, between 5 bar and 20 bar, or between 5 bar and 10 bar.

In other embodiments, the reaction pressure may reflect the pressure at which ethylene is added to the reactor. The ethylene may be added at a pressure such that the concentration of this reactant is sufficiently high in the solvent for optimal reaction rates. In some embodiments, the ethylene pressure is at least 10 psi, 50 psi, 75 psi, or 100 psi. In certain embodiments, the ethylene pressure is between 500 psi to 20,000 psi. At such partial pressures, the concentration of the ethylene reactant is sufficient high for optimal reaction rates. It should be understood that higher pressures can be used depending on the equipment available. In other embodiments, the ethylene is near critical where the temperature is between about 270K and about 290K, and the partial pressure of ethylene between about 45 bar and about 65 bar. In other embodiments, the ethylene is supercritical, where the temperature is greater than or equal to about 282K, and the partial pressure of ethylene is greater than about 734 psi. In yet other embodiments, the ethylene is supercritical, wherein the temperature is greater than or equal to about 282K and the partial pressure of ethylene is greater than or equal to about 734 psi.

It should be understood and clearly conveyed herein that the reaction temperature and reaction pressure may be the same as if each and every combination were individually listed. For example, in one variation, the method is carried out at a temperature of about 225° C. and a pressure of about 34 bar (equivalent to about 500 psi).

The methods described herein may also be carried out under supercritical conditions (e.g., supercritical pressures and/or supercritical temperatures). For example, in one embodiment, supercritical conditions may be used if a solvent is not used in the reaction. In one embodiment, the method is carried out at or above 50 bar and/or at or above 9° C. (i.e., 282 K).

It should be understood that temperature may be expressed as degrees Celsius (° C.) or Kelvin (K). One of ordinary skill in the art would be able to convert the temperature described herein from one unit to another. Pressure may also be expressed as gauge pressure (barg), which refers to the pressure in bars above ambient or atmospheric pressure. Pressure may also be expressed as bar, atmosphere (atm), pascal (Pa) or pound-force per square inch (psi). One of ordinary skill in the art would be able to convert the pressure described herein from one unit to another.

The method may be carried out batch-wise or continuously. The time of the reaction will also vary with the reaction conditions and desired yield, but is generally about 1 to 72 hours. In some of the foregoing embodiments, the reaction time is determined by the rate of conversion of the starting material. In some of the foregoing embodiments, the reaction mixture is reacted for 1 to 24 hours. In some of the foregoing embodiments, the reaction mixture is reacted for 1 to 10 hours. In some of the foregoing embodiments, the reaction mixture is reacted for 1 to 5 hours. In some of the foregoing embodiments, the reaction mixture is reacted for 1 to 3 hours. In some of the foregoing embodiments, the reaction mixture is reacted for less than 2 hours.

Isolation and Purification

The methods described herein may further include isolating para-xylene from the reaction mixture. Any methods known in the art may be employed to isolate the product. For example, para-xylene may be isolated by distillation.

In one exemplary embodiment, to isolate para-xylene from the reaction mixture, the reaction mixture can be first filtered to remove any solid catalysts and desiccants (if present). The filtered mixture may then be transferred to a distillation column. One of skill in the art would know how to recover para-xylene by distillation since the boiling points of the various components of the reaction mixture are known, including the boiling points of the solvents used. For example, in one embodiment where 1,4-dioxane is used, the solvent has a boiling point of 101° C. It is known in the art that para-xylene has a boiling point of 138° C.; HD has a boiling point of 191° C.; and DMF has a boiling point of 94° C. The solvent, HD, and/or DMF recovered can be recycled.

The methods described herein may also include purifying the isolated para-xylene. Any suitable methods known in the art may be employed to purify the isolated para-xylene, including for example column chromatography or recrystallization.

Yield, Conversion and Selectivity

The yield of a product takes into account the conversion of the starting materials into the product, and the selectivity for the product over other byproducts that may be formed.

The difference between yield, conversion and selectivity is explained in the examples provided below. For example, with respect to the conversion of HD into para-xylene, the reaction can be generalized as follows, where “A” represents the moles of HD; “B” represents the moles of ethylene; “C” represents the moles of para-xylene; “D” represents the moles of water produced; and “a”, “b”, “c” and “d” are stoichiometric coefficients. With respect to the conversion of DMF into para-xylene, the reaction can be generalized as follows, where “A” represents the moles of DMF; “B” represents the moles of ethylene; “C” represents the moles of para-xylene; “D” represents the moles of water produced; and “a”, “b”, “c” and “d” are stoichiometric coefficients. For example, with respect to the conversion of HD and DMF into para-xylene, the reaction can be generalized as follows, where “A” represents the total moles of HD and DMF; “B” represents the moles of ethylene; “C” represents the mole of para-xylene; “D” represents the moles of water produced; and “a”, “b”, “c” and “d” are stoichiometric coefficients. aA+bB→cC+dD,

Conversion of A is the percentage of reactant A that has been consumed during the reaction shown above, as expressed by the following equation:

${{\%\mspace{14mu}{Conversion}} = {\frac{{Ao} - {Af}}{Ao}*100\%}},$ where A_(o) is the initial number of moles of reactant A; and A_(f) is the final number of moles of reactant A.

Selectivity is the stoichiometrically relative amount of product C produced from the converted amount of reactant A, as expressed as a percentage by the following equation:

${{{Selectivity}\mspace{14mu}(\%)} = {\frac{{Cf}*\frac{a}{c}}{{Ao} - {Af}}*100\%}},$ where A_(o) is the starting moles of reactant A; A_(f) is the final number of moles of reactant A; and C_(f) is the number of moles of product C. In some embodiments where “a/c”=1, and the equation can be simplified to:

${{Selectivity}\mspace{14mu}(\%)} = {\frac{Cf}{{Ao} - {Af}}*100{\%.}}$

The yield of product C is the percentage of reactant A that is converted into product C, as expressed by the following equation: Yield(%)=Conversion(%)*Selectivity(%)

It should be understood that, when both DMF and HD are present, selectivity is calculated based on the amount of the molar sum of DMF and HD.

In certain embodiments, the methods described herein have a yield of at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 99% by weight. In other embodiments, the yield is between 10% to 100%, between 10% to 90%, between 20% to 80%, between 30% to 80%, between 40% to 80%, between 50%-80%, or between 60%-80% by weight.

In certain embodiments, the methods described herein have a selectivity of at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, or at least 99%. In other embodiments, the selectivity is between 40% to 99%, between 40% to 95%, between 40% to 90%, between 40% to 80%, between 50% to 99%, between 50% to 95%, between 50% to 90%, between 50% to 80%, between 60% to 99%, between 60% to 95%, between 60% to 90%, between 60% to 80%, between 70% to 99%, between 70% to 95%, between 70% to 90%, or between 70% to 80%.

Downstream Products

Para-xylene (PX or p-xylene) produced according to the methods described herein may be suitable for manufacture of one or more plastics, solvents or fuels. As discussed above, para-xylene can also be further oxidized to produce terephthalic acid. The terephthalic acid can be further processed to manufacture one or more plastics.

It should be understood that reference to “about” a value or parameter herein includes (and describes) embodiments that are directed to that value or parameter per se. For example, description referring to “about x” includes description of “x” per se. In other instances, the term “about” when used in association with other measurements, or used to modify a value, a unit, a constant, or a range of values, refers to variations of +/−10%.

It should also be understood that reference to “between” two values or parameters herein includes (and describes) embodiments that include those two values or parameters per se. For example, description referring to “between x and y” includes description of “x” and “y” per se.

EXAMPLES

The following Examples are merely illustrative and are not meant to limit any aspects of the present disclosure in any way.

Example 1 Preparation of PX from DMF

A mixture of 5.0 g of DMF, 0.025 g of copper triflate, and 100 mL of dioxane were charged to a high pressure autoclave fitted with a gas entrainment impeller. The autoclave was purged 3 times with nitrogen, once with ethylene, and then pressurized to 500 psig (3,447 kpas) with ethylene. The autoclave was heated to 250° C. at which point the pressure increased to 2250 psig (15,513 kpas). The reactor remained pressurized at 250° C. for 7 hours whereby the heater was turned off and the reactor was allowed to cool at RT The pressure was vented and the reaction solution was decanted into a storage bottle. The reaction mixture was a light yellow solution with a slight amount of black precipitate. The solution phase was analyzed by ¹H and ¹³C NMR spectroscopy, identifying residual DMF, PX, ethylene and HD as the major components together with dioxane as solvent. These components were quantified by ¹H NMR spectroscopy, the values being given in Table 1 below. Ethylene was observed in this sample at about 0.3 mole % by NMR.

The protocol in this Example was repeated for various catalysts, solvents and temperatures as specified in Table 1 below.

TABLE 1 Reaction Conditions Products Temp DMF DMF PX HD Catalyst Solvent (° C.) mol % mol % mol % mol % Conversion % Selectivity % Yield % Gd(OTf)₃ Dioxane 190 4.38 1.23 2.37 0.12 72 75 54 In(OTf)₃ Dioxane 190 3.43 0.73 2.18 0.39 79 80 63.2 AlCl₃ Dioxane 190 3.43 0.93 1.92 0.2 73 79 57.7 AlCl₃ Dioxane 220 3.43 0.08 2.99 0.12 98 89 87.2 Cu(OTf)₂ Dioxane 190 4.38 1.39 2.64 0.34 68 88 59.8 InCl₃ Dioxane 190 4.38 1.17 2.42 1.4 73 75 54.8 CuCl₂ Dioxane 190 4.38 1.57 2.45 4.6 64 87 55.7 CuCl₂ Dioxane 220 4.38 0.02 3.99 3.8 99.5 91.6 91.1 CuCl₂ Dioxane 250 4.38 0.28 3.94 1.73 91.8 98.0 90.0 Cu(OTf)₂ Dioxane 220 4.38 0.04 4.16 1.8 99.1 95.9 95.0 Cu(OTf)₂ Dioxane 250 4.38 0.04 4.32 0 98.9 99.6 98.5 Y(OTf)₃ Dioxane 220 4.38 0.13 3.87 2.2 97 91.1 88.4 Cu(OTf)₂ Triglyme 250 8.48 0 7.93 0 100 93.4 93.5 Mol % refers to mol % in dioxane, except for the HD which is calculated as the mol % of initial DMF

Example 2 Preparation of PX from DMF and HD

A mixture of 8.0 g of DMF, 2.0 g of HD, 0.5 g of yttrium triflate, and 200 g of dioxane were charged to a high pressure autoclave fitted with a gas entrainment impeller. The autoclave was purged 3 times with nitrogen, once with ethylene, and then pressurized to 500 psig (3,447 kpas) with ethylene. The autoclave was heated to 250° C. at which point the pressure increased to 2,000 psig (13,790 kpas). The reactor remained pressurized at 250° C. for 7 hours.

Samples were taken at hour intervals and analyzed by NMR spectroscopy for conversion and selectivity. After 7 hours, the heater was turned off and the reactor was allowed to cool to RT. The pressure was vented and the reaction solution was decanted into a storage bottle. A conversion of 100% was obtained after 7 hours with a molar selectivity to PX based on HD and DMF of 90%, yield equal to 90%.

Example 3 Preparation of PX from HD

A mixture of 5.0 g of HD, 0.05 g of copper triflate, and 100 g of dioxane were charged to a high pressure autoclave fitted with a gas entrainment impeller. The autoclave was purged 3 times with nitrogen, once with ethylene, and then pressurized to 500 psig (3,447 kpas) with ethylene. The autoclave was heated to 250° C. at which point the pressure increased to 1900 psig (13,100 kpas). The reactor remained pressurized at 250° C. for 7 hours. Samples were taken at hour intervals and analyzed by NMR spectroscopy for conversion and selectivity. After 7 hours, the heater was turned off and the reactor was allowed to cool to RT. The pressure was vented and the reaction solution was decanted into a storage bottle. A conversion of 94% was obtained after 7 hours with a molar selectivity to PX based on HD of 99%, yield equal to 93%.

Example 4 Comparative Example Comparison of PX Production from DMF Using Activated Carbon Versus Other Catalysts

A mixture of 10.0 g of DMF, 1.0 g of Norit Darco G60 activated carbon, 2.1 g of 3 Å molecular sieves (predried), and 200 g of dioxane were charged to a high pressure autoclave fitted with a gas entrainment impeller. The autoclave was purged 3 times with nitrogen, once with ethylene, and then pressurized to 460 psig (3,1712 kpas). The autoclave was heated to 190° C. at which point the pressure increased to 1270 psig (8,756 kpas). The reactor remained pressurized at 190° C. for 24 hours when the heater was turned off and the reactor was allowed to cool at RT. Prior to cooling, the pressure had decreased to 1240 psig (8,549 kpas). The pressure was vented and the reaction solution was decanted into a storage bottle. The reaction mixture was cloudy and black, but upon standing it clarified somewhat as the Norit settled. The solution was analyzed by ¹H and ¹³C NMR spectroscopy, identifying residual DMF, PX, ethylene and HD as the major components together with dioxane as solvent. These components were quantified by ¹H NMR spectroscopy, the values being given in Table A below. Very little conversion of DMF was observed, only 4.6%, and of that amount only 19% was converted to PX.

The protocol in this Comparative Example was repeated for various catalyst s, solvents and temperatures as specified in Table 2 below.

TABLE 2 Reaction Conditions Products Temp DMF DMF PX HD Catalyst Solvent (° C.) mol % mol % mol % mol % Conversion % Selectivity % Yield % Norit Darco G60 Dioxane 190 4.38 4.18 0.04 0.05 4.6 19 0.9 Cu(l)/Mordenite Dioxane 220 4.31 3.96 0.06 0.27 8 17.5 1.4 NiCl₂ Dioxane 190 4.38 3.93 0.25 1 10 56 5.6 Norit CA1 Dioxane 220 4.308 3.9 0.35 0.9 11.1 73 8.1 (H₃PO₄ Treated) Norit CA1 Dioxane 220 4.38 3.7 0.49 1.5 15.7 71.6 11.2 NiCl₂ Dioxane 190 4.38 3.93 0.25 1 10 56 5.6 CoCl₂ Dioxane 190 4.38 2.61 1.34 9.1 40 76 30.4 HY Zeolite Dioxane 190 5.42 2.38 1.5 0.37 56 49 27.4 ZnCl₂ Dioxane 190 4.38 3.23 0.91 ND 26 79 20.5 Y(OTf)₃ Sulfolane 250 5.88 0.70 2.13 ND 88.1 41.2 36.3 Y(OTf)₃ n-Methylpyrrolidone 250 3.57 0.14 3.21 0.00 97.1 67.6 65.6 Y(OTf)₃ Dimethylsulfoxide 250 3.76 Solvent decomposed, pressure increased sharply, and reaction was stopped Y(OTf)₃ Tetraethyleneglycol 250 9.18 1.01 3.03 2.68 86.4 38.2 33.0 Y(OTf)₃ Propylene Carbonate 250 4.85 Solvent decomposed, pressure increased sharply, and reaction was stopped Mol % refers to mol % in dioxane, except for the HD which is calculated as the mol % of initial DMF ND refers to “no data”

Example 5 Comparison of Supported Versus Unsupported Catalysts

This example compares the rate of reaction in converting DMF into PX using supported catalysts (e.g., CuCl₂ on alumina, CuCl₂ on HY Zeolite) versus unsupported catalysts (e.g., CuCl₂, Cu(OTf)₂, Y(OTf)₃).

A mixture of 10 g of DMF, catalyst (type and amount as specified in Table 3 below), and 200 g of dioxane were charged to a high pressure autoclave fitted with a gas entrainment impeller. The autoclave was purged 3 times with nitrogen, once with ethylene, and then pressurized to 500 psig (3,447 kpas) with ethylene. The autoclave was heated to 250° C. The reactor remained pressurized at 250° C. for 7 hours. Samples were taken at hour intervals and analyzed by NMR spectroscopy for conversion and selectivity. After 7 hours, the heater was turned off and the reactor was allowed to cool to RT. The pressure was vented and the reaction solution was decanted into a storage bottle. Conversion, molar selectivity, and yield for each catalyst are summarized in Table 3 below.

TABLE 3 Summary of data (10 g DMF, 200 g Dioxane, 250° C., 500 psig C₂H₄) Time to reach Amount of Conversion 50% Catalyst after 7 hrs Selectivity HD conversion Yield Catalyst (g) (mol %) (mol %) (mol %) (hrs) (mol %) CuCl₂ on 2.0 52 70 1.3 6.7 36.4 Alumina CuCl₂ on 2.0 77 82 1.3 2.6 63.1 HY Zeolite CuCl₂ 1.0 97 91 0.6 1.1 88.3 Cu(OTf)₂ 0.5 100 86 0.0 1.3 86.0 Y(OTf)₃ 0.5 99 84 0.0 1.0 83.2

Based on the results of Table 3 above, the non-supported catalysts were observed to convert DMF into PX faster than the supported catalysts.

Example 6 Comparison of Types and Amounts of Different Catalysts

This example compares the rate of reaction in converting DMF into PX using varying amounts of catalyst.

The protocol described in Example 5 above for converting DMF into PX was used for three different catalysts (i.e., CuCl₂, Cu(OTf)₂, and Y(OTf)₃), according to the conditions set forth in Tables 4, 5, and 6 below, respectively. Conversion, molar selectivity, and yield for each catalyst are also summarized in each table below.

TABLE 4 Summary of CuCl₂ (10 g DMF, 200 g Dioxane, 250° C., 500 psig C₂H₄) Time to reach Conversion HD 50% Catalyst after 7 hrs Selectivity (mol conversion Yield Catalyst (g) (mol %) (mol %) %) (hrs) (mol %) CuCl₂ 0.10 70 101 3.2 3.5 70 CuCl₂ 0.10 65 98 3.2 4.2 64 (rerun) CuCl₂ 0.50 92 98 1.7 1.5 90 CuCl₂ 1.00 97 91 1.0 1.1 88

TABLE 5 Summary of Cu(OTf)₂ data (250° C., 500 psig C₂H₄) Time to Conversion HD reach 50% Catalyst DMF Dioxane after 7 hrs Selectivity (mol conversion Yield Catalyst (g) (g) (g) (mol %) (mol %) %) (hrs) (mol %) Cu(OTf)₂ 0.025 5 100 99 100 0.1 0.3 99 Cu(OTf)₂ 0.05 10 200 98 100 0.5 1.0 98 Cu(OTf)₂ 0.10 10 200 100 95 0.0 1.0 95 Cu(OTf)₂ 0.10 10 200 99 101 0.1 1.2 100 (rerun) Cu(OTf)₂ 0.50 10 200 100 86 0.0 1.3 86

TABLE 6 Summary of Y(OTf)₃ data (10 g DMF, 200 g Dioxane, 250° C., 500 psig C₂H₄) Conversion Catalyst after 7 hrs Selectivity HD Time to reach 50% Yield Catalyst (g) (mol %) (mol %) (mol %) conversion (hrs) (mol %) Y(OTf)₃ 0.50 99 84 0.0 1.1 84 Y(OTf)₃ 0.25 100 92 0.4 1.1 92 Y(OTf)₃ 0.10 98 94 0.4 1.3 92

Example 7 Comparison of Solvent Concentration

This examples compares the rate of reaction in converting DMF into PX using different concentrations of dioxane as the solvent.

The protocol described in Example 5 above for converting DMF into PX was used according to the conditions set forth in Table 7 below. The samples taken from the reaction phase were each separated. The phases observed were an upper, opaque, PX-rich phase, and a lower water/dioxane phase. Conversion, molar selectivity, and yield for each catalyst are also summarized in Table 7 below.

TABLE 7 Summary of solvent concentration data (0.5 g Y(OTf)₃, 200 g Dioxane, 250° C., 500 psig C₂H₄) Conversion Time to reach after 7 hrs Selectivity HD 50% conversion Yield Catalyst DMF (g) (mol %) (mol %) (mol %) (hrs) (mol %) Y(OTf)₃ 20 100 85 0.1 0.8 85 Y(OTf)₃ 10 99 84 0.0 1.1 83

Example 8 Comparison of Solvent Types

This examples compares the rate of reaction in converting DMF into PX using different solvents, including dioxane, triglyme, triethylene glycol (TEG), N-methylpyrrole (NMP), sulfolane, propylene carbonate, and dimethylsulfoxide (DMSO).

The protocol described in Example 5 above for converting DMF into PX was used according to the conditions set forth in Table 8 below. Conversion, molar selectivity, and yield for each catalyst for dioxane, TEG, sulfolane, triglyme and NMP are also summarized in Table 8 below. Propylene carbonate was observed to be unstable at 250° C. and appeared to have degraded into CO₂. Similarly, DMSO was also unstable at 250° C. and appeared to have degraded. As such, the reactions using propylene carbonate and DMSO were not sampled.

TABLE 8 Summary of solvent data (0.5 g Y(OTf)₃, 10 g DMF, 250° C., 500 psig C₂H₄) Time to Conversion HD reach 50% Yield Solvent after 7 hrs Selectivity (mol conversion (mol Solvent (g) (mol %) (mol %) %) (hrs) %) Dioxane 200 99 84 0.0 1.1 84 TEG 200 100 27 0.0 <<1.0 27 Sulfolane 200 88 41 0.0 ND 36 Triglyme 200 99 81 0.0 0.9 81 NMP 200 97 68 0.0 <<1.0 66 ND refers to “no data”

Based on the data in Table 8, dioxane and triglyme were observed to have similar reaction kinetics in converting DMF into PX. NMP was also observed to be a suitable solvent for converting DMF into PX.

Example 9 Comparison of Solvents for Improving PX Selectivity

This examples compares the rate of reaction in converting DMF into PX using different solvents and catalysts s. The solvents used include triglyme and triethylene glycol (TEG). The catalysts s include Cu(OTf)₂ and Y(OTf)₃.

The protocol described in Example 5 above for converting DMF into PX was used according to the conditions set forth in Tables 9 and 10 below. Conversion, molar selectivity, and yield for each catalyst for each solvent/catalyst combinations are summarized in the tables below.

TABLE 9 Summary of triglyme data (10 g DMF, 250° C., 500 psig C₂H₄) Time to reach Conversion 50% Yield Catalyst Triglyme after 7 hrs Selectivity HD (mol conversion (mol Catalyst (g) (g) (mol %) (mol %) %) (hrs) %) Cu(OTf)₂ 0.05 200 100 94 0.0 1.1 94 Y(OTf)₃ 0.50 200 99 82 0.0 0.9 81

TABLE 10 Summary of TEG data (500 psig C₂H₄) Time to Conversion HD reach 50% Yield Catalyst TEG DMF Temp after 7 hrs Selectivity (mol conversion (mol Catalyst (g) (g) (g) (° C.) (mol %) (mol %) %) (hrs) %) Y(OTf)₃ 0.05 100 5 220 86 38 3.0 1.0 33 Y(OTf)₃ 0.50 200 10 250 100 27 0.0 <<1.0 27

Based on the data in Table 9 above, triglyme as the solvent and Cu(OTf)₂ as the catalyst showed comparable reaction kinetics in converting DMF to PX as dioxane as the solvent and Cu(OTf)₂ as the catalyst (based on the data in Table 5 of Example 6 above).

Example 10 Comparison of Temperature

This example compares the rate of reaction in converting DMF into PX at different temperatures. The protocol described in Example 5 above for converting DMF into PX was used according to the temperatures set forth in Table 11 below. The reactions in this example used 10 g DMF, 1.0 g CuCl₂, 200 g dioxane, and 500 psig C₂H₄. Conversion and molar selectivity, and yield are summarized in Table 11 below.

TABLE 11 Summary of temperature data (1.0 g CuCl₂, 10 g DMF, 200 g Dioxane, 500 psig C₂H₄) Time to Conversion reach 50% Temperature after 7 hrs Selectivity HD conversion Yield (° C.) (mol %) (mol %) (mol %) (hrs) (mol %) 180 22 72 5.5 23 16 250 96 91 1.0 1.2 88

Temperature was observed to have a effect on the kinetics of the reaction. For the reaction to take place with around 90% conversion in a reasonable amount of time, temperatures close to 250° C. should be used. Lowering the reaction temperature surprisingly did not increase selectivity, as selectivity was observed to increase with time and conversion in the 180° C. reaction at the end of 7 hours.

Example 11 Comparison of Pressure

This example compares the rate of reaction in converting DMF into PX at different pressures. The protocol described in Example 5 above for converting DMF into PX was used according to the conditions set forth in Tables 12 and 13 below. The solvent used in this example was dioxane, and the catalysts used were CuCl₂ and Y(OTf)₃. Conversion, molar selectivity, and yield for each catalyst for each catalyst/pressure combination is summarized in the tables below.

TABLE 12 Summary of Y(OTf)₃/pressure data (0.5 g Y(OTf)₃, 10 g DMF, 200 g dioxane, 250° C. Time to Conversion reach 50% Pressure after 7 hrs Selectivity HD conversion Yield (psig) (mol %) (mol %) (mol %) (hrs) (mol %) 300 97 87 0.5 1.6 85 500 99 84 0.0 1.0 83 550 100 90 0.0 1.0 90

TABLE 13 Summary of CuCl₂/pressure data (1.0 g CuCl₂, 10 g DMF, 200 g dioxane, 180° C.) Time to Conversion reach 50% Pressure after 7 hrs Selectivity HD conversion Yield (psig) (mol %) (mol %) (mol %) (hrs) (mol %) 500 22 72 5.5 23 16 700 33 64 2.7 11 21

Example 12 PX Production from HD

This example demonstrates the conversion of HD into PX. The protocol described in Example 5 was used in for HD (2 g) as the starting material. Y(OTf)₃ (0.5 g) was used as the catalyst, dioxane (200 g) as the solvent. Ethylene was provided at 500 psig, and the reaction temperature was 250° C. Conversion, molar selectivity, and yield are summarized Table 14 below.

TABLE 14 Summary of HD data Time to Conversion reach 50% after 7 hrs Selectivity HD conversion Yield (mol Catalyst (mol %) (mol %) (mol %) (hrs) %) Y(OTf)₃ 100 90 0.0 0.9 90

Based on the data in Table 14 above, HD was observed convert into PX with a selectivity of about 99% was observed for Y(OTf)₃ as the catalyst.

As a control, a reaction using HD with no ethylene or catalyst (5 g HD, 100 g dioxane, 250° C.) was performed. HD was not observed to convert to DMF without the presence of a catalyst. Additionally, HD with a catalyst but no ethylene (5 g HD, 0.25 g Y(OTf)₃, 100 g Dioxane, 250° C.) was also performed. After 1 hour of reaction time, 86% of HD was converted with 62% selectivity to DMF.

Example 13 Comparison Using Heteropolyacids

This examples compares the rate of reaction in converting DMF into PX using heteropolyacid catalysts. The protocol described in Example 5 was used in for each catalyst and solvent along with the reaction conditions as summarized in Table 15 below. PX yield for each reaction is also provided in Table 15 below.

TABLE 15 Summary of HPAs data (10 g DMF, 0.5 g catalyst, 200 g solvent, 250° C., 500 psig C₂H₄) Conversion after 7 hrs Selectivity Yield Catalyst Solvent (mol %) (mol %) (mol %) 12-molybdosilicic acid Dioxane 98.8 84.8 83.8 hydrate [MoO₃][H₃PO₄]•H₂O Dioxane 97.9 84.8 77.1 12-molybdosilicic acid Triglyme n/a n/a ND ND = NMR spectrum was not run

Example 14 Comparison Using Various Solvents

This examples compares the rate of reaction in converting DMF into PX using aliphatic solvents, and mixtures of solvents. The protocol described in Example 5 was used in for each catalyst and solvent along with the reaction conditions as summarized in Tables 16 below and 17. PX yield for each reaction is also provided in Tables 16 and 17 below.

TABLE 16 Summary of solvent data (10 g DMF, 0.5 g catalyst, 200 g solvent, 250° C., 500 psig C₂H₄) Conversion after 7 hrs Selectivity Yield Catalyst Solvent (mol %) (mol %) (mol %) Cu (II Dioxane 98.6 96.0 94.7 bis(trifluoro- methyl- sulfonyl)imide Cu(OTf)₂ Dioxane 100.0  85.8 85.8 Cu(OTf)₂ Water n/a n/a Phase separated and not quantified Cu(OTf)₂ Dodecane 92.1 85.9 79.1 Cu(OTf)₂ Dioxane + 99.4 92.2 91.6 Dodecane

TABLE 17 Summary of aliphatic solvent data Catalyst DMF Solvent Temp Pressure Conversion Selectivity Catalyst (g) (g) Solvent (g) (° C.) (psi) (molar) (molar) Cu(OTf)₂ 0.1 30.01 n-Heptane 60.01 200 2100  74.1 ND Dioxane 0.1 Cu(OTf)₂ 2.51 20.01 Dodecane 30.01 250 1550-1575 99.7 52.4 Cu(OTf)₂ 0.1 30.01 Decane 60.01 250 2275-1900 94.6 98.4 Cu(OTf)₂ 0.15 21.0 Dodecane 30.01 250 650 93.0 101.9 Cu(OTf)₂ 0.15 20.0 Dodecane 30.00 250 800 93.4 102.7 Dioxane 0.1 ND = quantification of selectivity not available, but PX was observed as a product

Example 15 Comparison Using Copper-Containing Salt Catalysts

This examples compares the rate of reaction in converting DMF into PX using metal-containing salt catalysts, such as copper acetate and copper acetylacetonate. The protocol described in Example 5 was used in for each catalyst and solvent along with the reaction conditions as summarized in Table 18 below. PX yield for each reaction is also provided in Table 18 below.

TABLE 18 Summary of copper-containing salt catalyst data (2.5 g DMF, 50 g dioxane, 0.125 g catalyst, 250° C., 1500-1600 psig) Copper-containing salt Conversion Selectivity catalyst (molar) (molar) copper acetate 85.9 ND copper acetylacetonate 80.1 94.5 ND = quantification of selectivity not available, but PX was observed as a product 

What is claimed:
 1. A method for producing para-xylene, comprising: combining 2,5-hexanedione, ethylene, and catalyst to form a reaction mixture, wherein the catalyst is copper chloride, copper triflate, yttrium triflate, a heteropolyacid, or η²-ethylene-copper(II)triflate; and producing para-xylene from at least a portion of the 2,5-hexanedione and ethylene in the reaction mixture.
 2. The method of claim 1, further comprising isolating para-xylene from the reaction mixture.
 3. The method of claim 1, wherein the 2,5-hexanedione, the ethylene, and the catalyst are further combined with a solvent system to form the reaction mixture.
 4. The method of claim 3, wherein the solvent system comprises an aprotic solvent.
 5. The method of claim 3, wherein the solvent system comprises an ether solvent.
 6. The method of claim 3, wherein the solvent system comprises a C1-C20 aliphatic solvent, a C6-C20 aromatic solvent, an alkyl phenyl solvent, a C2-C20 ether, a C2-C20 ester, a C1-C20 alcohol, a C2-C20 ketone, or any combinations or mixtures thereof.
 7. The method of claim 3, wherein the solvent system comprises dimethylacetamide, acetonitrile, sulfolane, dioxane, dioxane, dimethyl ether, diethyl ether, glycol dimethyl ether (monoglyme), ethylene glycol diethyl ether (ethyl glyme), diethylene glycol dimethyl ether (diglyme), diethylene glycol diethyl ether (ethyl digylme), triethylene glycol dimethyl ether (triglyme), diethylene glycol dibutyl ether (butyl diglyme), tetraethylene glycol dimethyl ether (tetraglyme), polyglyme, proglyme, highlyme, tetrahydrofuran, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, triacetin, dibutylphthalate, butane, pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane, nonane, decane, undecane, dodecane, hexadecane, tetrachloride, chloroform, dichloromethane, nitromethane, toluene, anisole, nitrobenzene, bromobenzene, N-methylpyrrole, para-xylene, mesitylene, dodecylbenzene, pentylbenzene, hexylbenzene, diphenyl ether, methyldiphenyl ether, ethyldiphenyl ether, water, or any combinations or mixtures thereof.
 8. The method of claim 3, wherein the solvent system comprises dioxane, glyme, diglyme, triglyme, decane, dodecane, para-xylene, or any combinations or mixtures thereof.
 9. The method of claim 8, wherein the solvent system comprises para-xylene.
 10. The method of claim 1, wherein the catalyst is copper chloride, copper triflate, or yttrium triflate.
 11. The method of claim 1, wherein the catalyst is a heteropolyacid.
 12. The method of claim 1, wherein the catalyst is η²-ethylene-copper(II)triflate.
 13. The method of claim 3, wherein the solvent system comprises an ether, a C₈₊ alkyl solvent, or para-xylene.
 14. The method of claim 1, wherein the catalyst is copper chloride, copper triflate, or yttrium triflate; and the solvent system comprises dioxane, dodecane, para-xylene, or any mixtures or combinations thereof.
 15. The method of claim 1, wherein at least a portion of the 2,5-hexanedione and ethylene are converted to para-xylene at a temperature of at least 150° C.
 16. The method of claim 15, wherein at least a portion of the 2,5-hexanedione and ethylene are converted to para-xylene at a temperature of between 150° C. and 300° C.
 17. The method of claim 1, wherein the catalyst is copper chloride.
 18. The method of claim 1, wherein the catalyst is copper triflate.
 19. The method of claim 1, wherein the catalyst is yttrium triflate.
 20. The method of claim 3, wherein the solvent system comprises aliphatic solvent.
 21. The method of claim 3, wherein the solvent system comprises alkyl phenyl solvent.
 22. The method of claim 15, wherein at least a portion of the 2,5-hexanedione and ethylene are converted to para-xylene at a temperature of between 200° C. and 400° C. 